1. Field of the Invention
The present invention relates to a wafer and a package product manufacturing method.
2. Description of the Related Art
In recent years, package products have been widely used which include: a base substrate and a lid substrate that are stacked on and anodically bonded to each other with a cavity formed therebetween; and an operation piece mounted on a portion of the base substrate located in the cavity. One known example of this type of package product is a piezoelectric vibrator attached to a mobile phone or personal digital assistant, which utilizes a quartz or the like as a time source, timing source for control signal or the like, reference signal source or the like.
By the way, this package product is formed as follows, for example, as described in Patent Document 1 below.
First, a base substrate wafer and a lid substrate wafer are set in an anodic bonding apparatus placed in a vacuum chamber, then these wafers are stacked on each other with a bonding film for anodic bonding, of a conductive material, provided therebetween.
Here, on the bonding surface of the lid substrate wafer, a plurality of concave portions are formed each of which will be the cavity when the base substrate wafer is stacked thereon. On the other hand, on the bonding surface of the base substrate wafer, a plurality of operation pieces are mounted corresponding to the concave portions, and the bonding film is formed on the portion other than the portions in which the operation pieces are mounted. Further, the lid substrate wafer is set on a electrode plate of the anodic bonding apparatus.
Next, while the lid substrate wafer is being heated to activate ions contained therein, a voltage is applied between the bonding film and the electrode plate to cause a current to flow in the lid substrate wafer, thereby causing an electrochemical reaction in the interface between the bonding film and the bonding surface of the lid substrate wafer to anodically bond them, forming a bonded wafer body.
Then, this bonded wafer body is cut at predetermined locations to form a plurality of package products.
Patent Document 1: JP-A-2006-339896
Conventionally, however, when the above-described anodic bonding is performed, in the product area in which the concave portions (cavities) or operation pieces are placed, the outer circumference portions of the wafers tend to be bonded before the central portions are bonded. Then, oxygen gas generated between the wafers in this bonding may remain between the central portions to reduce the vacuum in the cavities of the package products obtained from the central portions, which may provide a package product lacking in desired performance.
In view of the above, it is an object of the present invention to provide a wafer and a package product manufacturing method in which oxygen gas generated between the two wafers when the wafers are bonded can be facilitated to be discharged to the outside.